Over the last few decades, the semiconductor industry has undergone a revolution by the use of semiconductor technology to fabricate small, highly integrated electronic devices, and the most common semiconductor technology presently used is silicon-based. A large variety of semiconductor devices have been manufactured having various applications in numerous disciplines. One silicon-based semiconductor device is a transistor. The transistor is one of the basic building blocks of most modern electronic circuits. Importantly, these electronic circuits realize improved performance and lower costs, as the performance of the transistor is increased and as manufacturing costs are reduced.
A typical transistor includes a bulk semiconductor substrate on which a gate electrode is disposed. The gate electrode, which acts as a conductor, receives an input signal to control operation of the device. Source and drain regions are typically formed in regions of the substrate adjacent the gate electrodes by doping the regions with a dopant of a desired conductivity. The conductivity of the doped region depends on the type of impurity used to dope the region. The typical transistor is symmetrical, in that the source and drain are interchangeable. Whether a region acts as a source or drain typically depends on the respective applied voltages and the type of device being made. The collective term source/drain region is used herein to generally describe an active region used for the formation of either a source or drain. Associated with source/drain regions are source/drain extensions that are formed adjacent the source/drain regions and reduce a channel length of the transistor.
Transistors with shallow and ultra-shallow source/drain extensions have become more difficult to manufacture. Forming source/drain extensions with junction depths of less than 30 nm is very difficult using conventional fabrication techniques. Conventional ion implantation and diffusion-doping techniques make transistors susceptible to short-channeling effects. Additionally, conventional ion implantation techniques have difficulty maintaining shallow source and drain extensions because point defects generated in the bulk semiconductor substrate during ion implantation can cause the dopant to more easily diffuse. The presence of excess silicon interstitials in the vicinity of an implanted dopant distribution such as boron causes an effect known as transient enhanced diffusion (TED).
TED is characterized by a gradient in the concentration profile of excess interstitials that causes a large enhancement in dopant diffusion rate in the “downhill” direction of the negative gradient. The effect is short in duration, lasting only several minutes at temperatures as low as 800° C., and only seconds at higher temperatures, until the excess interstitials recombine or are otherwise removed from the vicinity of the dopant. However, during this short period, the effective diffusivity of the dopants can be enhanced by a factor of more than 10,000. As the damage peak is positioned slightly shallower than the dopant peak, the enhanced diffusion tends to shift the dopants deeper into the silicon. As a result, the movement of the dopants due to the damage created by the implant process is a primary factor in determining the final junction depths and profile shapes of the source/drain regions.
Continued miniaturization of semiconductor devices necessitates reliable formation of ultra shallow source/drain extension. Accordingly, there exists a need for semiconductor device and method of manufacture that provides low-resistance, shallow source/drain extensions with reduced short-channeling effects and reduced transient enhanced diffusion.